# netdevice - low-level access to Linux network devices - man(7) - [phpMan] [_netdevice_(7)](https://www.chedong.com/phpMan.php/man/netdevice/7/markdown) Miscellaneous Information Manual [_netdevice_(7)](https://www.chedong.com/phpMan.php/man/netdevice/7/markdown) ## NAME netdevice - low-level access to Linux network devices ## SYNOPSIS ### #include ### #include ## DESCRIPTION This man page describes the sockets interface which is used to configure network devices. Linux supports some standard ioctls to configure network devices. They can be used on any socket's file descriptor regardless of the family or type. Most of them pass an _ifreq_ struc‐ ture: struct ifreq { char ifr_name[IFNAMSIZ]; /* Interface name */ union { struct sockaddr ifr_addr; struct sockaddr ifr_dstaddr; struct sockaddr ifr_broadaddr; struct sockaddr ifr_netmask; struct sockaddr ifr_hwaddr; short ifr_flags; int ifr_ifindex; int ifr_metric; int ifr_mtu; struct ifmap ifr_map; char ifr_slave[IFNAMSIZ]; char ifr_newname[IFNAMSIZ]; char *ifr_data; }; }; **AF_INET6 **is an exception. It passes an _in6_ifreq_ structure: struct in6_ifreq { struct in6_addr ifr6_addr; u32 ifr6_prefixlen; int ifr6_ifindex; /* Interface index */ }; Normally, the user specifies which device to affect by setting _ifr_name_ to the name of the interface or _ifr6_ifindex_ to the index of the interface. All other members of the structure may share memory. ### Ioctls If an ioctl is marked as privileged, then using it requires an effective user ID of 0 or the **CAP_NET_ADMIN **capability. If this is not the case, **EPERM **will be returned. **SIOCGIFNAME** Given the _ifr_ifindex_, return the name of the interface in _ifr_name_. This is the only ioctl which returns its result in _ifr_name_. **SIOCGIFINDEX** Retrieve the interface index of the interface into _ifr_ifindex_. **SIOCGIFFLAGS** **SIOCSIFFLAGS** Get or set the active flag word of the device. _ifr_flags_ contains a bit mask of the following values: Device flags IFF_UP Interface is running. IFF_BROADCAST Valid broadcast address set. IFF_DEBUG Internal debugging flag. IFF_LOOPBACK Interface is a loopback interface. IFF_POINTOPOINT Interface is a point-to-point link. IFF_RUNNING Resources allocated. IFF_NOARP No arp protocol, L2 destination address not set. IFF_PROMISC Interface is in promiscuous mode. IFF_NOTRAILERS Avoid use of trailers. IFF_ALLMULTI Receive all multicast packets. IFF_MASTER Master of a load balancing bundle. IFF_SLAVE Slave of a load balancing bundle. IFF_MULTICAST Supports multicast IFF_PORTSEL Is able to select media type via ifmap. IFF_AUTOMEDIA Auto media selection active. IFF_DYNAMIC The addresses are lost when the interface goes down. IFF_LOWER_UP Driver signals L1 up (since Linux 2.6.17) IFF_DORMANT Driver signals dormant (since Linux 2.6.17) IFF_ECHO Echo sent packets (since Linux 2.6.25) Setting the active flag word is a privileged operation, but any process may read it. **SIOCGIFPFLAGS** **SIOCSIFPFLAGS** Get or set extended (private) flags for the device. _ifr_flags_ contains a bit mask of the following values: Private flags IFF_802_1Q_VLAN Interface is 802.1Q VLAN device. IFF_EBRIDGE Interface is Ethernet bridging device. IFF_SLAVE_INACTIVE Interface is inactive bonding slave. IFF_MASTER_8023AD Interface is 802.3ad bonding master. IFF_MASTER_ALB Interface is balanced-alb bonding master. IFF_BONDING Interface is a bonding master or slave. IFF_SLAVE_NEEDARP Interface needs ARPs for validation. IFF_ISATAP Interface is RFC4214 ISATAP interface. Setting the extended (private) interface flags is a privileged operation. **SIOCGIFADDR** **SIOCSIFADDR** **SIOCDIFADDR** Get, set, or delete the address of the device using _ifr_addr_, or _ifr6_addr_ with _ifr6_prefixlen_. Setting or deleting the interface address is a privileged operation. For compatibility, **SIOCGIFADDR **returns only **AF_INET **addresses, **SIOCSIFADDR **accepts **AF_INET **and **AF_INET6 **addresses, and **SIOCDIFADDR **deletes only **AF_INET6 **addresses. A **AF_INET **address can be deleted by setting it to zero via **SIOCSIFADDR**. **SIOCGIFDSTADDR** **SIOCSIFDSTADDR** Get or set the destination address of a point-to-point device using _ifr_dstaddr_. For compatibility, only **AF_INET **addresses are accepted or returned. Setting the destina‐ tion address is a privileged operation. **SIOCGIFBRDADDR** **SIOCSIFBRDADDR** Get or set the broadcast address for a device using _ifr_brdaddr_. For compatibility, only **AF_INET **addresses are accepted or returned. Setting the broadcast address is a privileged operation. **SIOCGIFNETMASK** **SIOCSIFNETMASK** Get or set the network mask for a device using _ifr_netmask_. For compatibility, only **AF_INET **addresses are accepted or returned. Setting the network mask is a privileged operation. **SIOCGIFMETRIC** **SIOCSIFMETRIC** Get or set the metric of the device using _ifr_metric_. This is currently not imple‐ mented; it sets _ifr_metric_ to 0 if you attempt to read it and returns **EOPNOTSUPP **if you attempt to set it. **SIOCGIFMTU** **SIOCSIFMTU** Get or set the MTU (Maximum Transfer Unit) of a device using _ifr_mtu_. Setting the MTU is a privileged operation. Setting the MTU to too small values may cause kernel crashes. **SIOCGIFHWADDR** **SIOCSIFHWADDR** Get or set the hardware address of a device using _ifr_hwaddr_. The hardware address is specified in a struct _sockaddr_. _sa_family_ contains the ARPHRD_* device type, _sa_data_ the L2 hardware address starting from byte 0. Setting the hardware address is a priv‐ ileged operation. **SIOCSIFHWBROADCAST** Set the hardware broadcast address of a device from _ifr_hwaddr_. This is a privileged operation. **SIOCGIFMAP** **SIOCSIFMAP** Get or set the interface's hardware parameters using _ifr_map_. Setting the parameters is a privileged operation. struct ifmap { unsigned long mem_start; unsigned long mem_end; unsigned short base_addr; unsigned char irq; unsigned char dma; unsigned char port; }; The interpretation of the ifmap structure depends on the device driver and the archi‐ tecture. **SIOCADDMULTI** **SIOCDELMULTI** Add an address to or delete an address from the device's link layer multicast filters using _ifr_hwaddr_. These are privileged operations. See also [**packet**(7)](https://www.chedong.com/phpMan.php/man/packet/7/markdown) for an alter‐ native. **SIOCGIFTXQLEN** **SIOCSIFTXQLEN** Get or set the transmit queue length of a device using _ifr_qlen_. Setting the transmit queue length is a privileged operation. **SIOCSIFNAME** Changes the name of the interface specified in _ifr_name_ to _ifr_newname_. This is a privileged operation. It is allowed only when the interface is not up. **SIOCGIFCONF** Return a list of interface (network layer) addresses. This currently means only ad‐ dresses of the **AF_INET **(IPv4) family for compatibility. Unlike the others, this ioctl passes an _ifconf_ structure: struct ifconf { int ifc_len; /* size of buffer */ union { char *ifc_buf; /* buffer address */ struct ifreq *ifc_req; /* array of structures */ }; }; If _ifc_req_ is NULL, **SIOCGIFCONF **returns the necessary buffer size in bytes for receiv‐ ing all available addresses in _ifc_len_. Otherwise, _ifc_req_ contains a pointer to an array of _ifreq_ structures to be filled with all currently active L3 interface ad‐ dresses. _ifc_len_ contains the size of the array in bytes. Within each _ifreq_ struc‐ ture, _ifr_name_ will receive the interface name, and _ifr_addr_ the address. The actual number of bytes transferred is returned in _ifc_len_. If the size specified by _ifc_len_ is insufficient to store all the addresses, the ker‐ nel will skip the exceeding ones and return success. There is no reliable way of de‐ tecting this condition once it has occurred. It is therefore recommended to either determine the necessary buffer size beforehand by calling **SIOCGIFCONF **with _ifc_req_ set to NULL, or to retry the call with a bigger buffer whenever _ifc_len_ upon return dif‐ fers by less than _sizeof(struct_ _ifreq)_ from its original value. If an error occurs accessing the _ifconf_ or _ifreq_ structures, **EFAULT **will be returned. Most protocols support their own ioctls to configure protocol-specific interface options. See the protocol man pages for a description. For configuring IP addresses, see [**ip**(7)](https://www.chedong.com/phpMan.php/man/ip/7/markdown). In addition, some devices support private ioctls. These are not described here. ## NOTES **SIOCGIFCONF **and the other ioctls that accept or return only **AF_INET **socket addresses are IP- specific and perhaps should rather be documented in [**ip**(7)](https://www.chedong.com/phpMan.php/man/ip/7/markdown). The names of interfaces with no addresses or that don't have the **IFF_RUNNING **flag set can be found via _/proc/net/dev_. **AF_INET6 **IPv6 addresses can be read from _/proc/net/if_inet6_ or via [**rtnetlink**(7)](https://www.chedong.com/phpMan.php/man/rtnetlink/7/markdown). Adding a new IPv6 address and deleting an existing IPv6 address can be done via **SIOCSIFADDR **and **SIOCD‐** **IFADDR **or via [**rtnetlink**(7)](https://www.chedong.com/phpMan.php/man/rtnetlink/7/markdown). Retrieving or changing destination IPv6 addresses of a point-to- point interface is possible only via [**rtnetlink**(7)](https://www.chedong.com/phpMan.php/man/rtnetlink/7/markdown). ## BUGS glibc 2.1 is missing the _ifr_newname_ macro in __. Add the following to your program as a workaround: #ifndef ifr_newname #define ifr_newname ifr_ifru.ifru_slave #endif ## SEE ALSO [**proc**(5)](https://www.chedong.com/phpMan.php/man/proc/5/markdown), [**capabilities**(7)](https://www.chedong.com/phpMan.php/man/capabilities/7/markdown), [**ip**(7)](https://www.chedong.com/phpMan.php/man/ip/7/markdown), [**rtnetlink**(7)](https://www.chedong.com/phpMan.php/man/rtnetlink/7/markdown) Linux man-pages 6.7 2023-10-31 [_netdevice_(7)](https://www.chedong.com/phpMan.php/man/netdevice/7/markdown)